EP0811155B1 - Process for determining the surface state of highways in particular, and device for carrying out this process - Google Patents

Abstract

PCT No. PCT/DE96/00347 Sec. 371 Date Oct. 22, 1997 Sec. 102(e) Date Oct. 22, 1997 PCT Filed Feb. 23, 1996 PCT Pub. No. WO96/26430 PCT Pub. Date Aug. 29, 1996There are proposed a method and a device for ascertaining the surface condition, particularly of traffic routes, as regards dryness, wetness or icing, in which the surface is irradiated by a radiation source with an infrared component, and the reflected radiation is measured simultaneously in different wavelength ranges characterizing water and ice. In this case at least four wavelength ranges are selected, permitting sufficient depth or penetration of the radiation into the surface. A first and a second wavelength range are so selected that they are influenced to a very small degree by absorption of the water molecules, and a third and fourth wavelength ranges are so selected that they are characteristic for water and ice. The influence of the background on signals measured in the third and fourth wavelength ranges is compensated for by means of the information in the signals measured in the first and second wavelength ranges. In dependence on the measured signals, therefore, a prediction can be made regarding the surface condition.

Description

The invention relates to a method for Determining the surface condition, in particular of traffic routes, according to the preamble of the main claim and on a device for performing of the procedure.

DE 40 08 280 describes a method for non-contact Determination of the road surface condition regarding dryness, wetness or icing known in which the surface to be examined with a broadband light source and that reflected light selectively in two wavelength ranges is measured simultaneously. The measuring wavelengths lie in a wavelength range in which the reflection behavior a spectral dependence shows from the surface state, namely in the wavelength range from 2700 nm to 3200 nm, of which Signals at two wavelengths in this wavelength range the quotient is formed which is the surface state characterized. The determined one Signal quotient becomes one of the states dry, wet or icy assigned.

The known method has the disadvantage that only the direct surface is considered and not the state just below the surface. As a consequence, that freezing over or under freezing is not recognized can be because at the wavelengths from 2700 nm to 3200 nm the penetration depth of the electromagnetic Radiation in the surface is extremely low. Especially is also stated in the publication, that regardless of the layer thickness, the detection of the Surface condition should be provided.

The invention has for its object a method to determine the surface condition in particular of traffic routes with regard to drought, Wetness or icing and a corresponding device to create that cost-effectively to implement are and a quick and accurate determination of the Surface condition also in deeper layers of the Allow surface.

This object is achieved by the characterizing Features of the main claim related solved with the features of the generic term. Beneficial Developments and refinements of this task solution arise for the procedure as well the one required to carry out the procedure Device from the subclaims.

With the present inventive method it is possible for the first time, a practically instantaneous detection of ice and frost formation on solid surfaces, such as Road surfaces, using spectral analysis measurement even when considering the layer thickness of the surface to be determined, depending on the respective degree of crystallization, the liquid does not have to be exclusively water, but it is also another solidified protic Can act liquid or solution, for example also by a freezing point Salt water solution. The degree of crystallization of the water or the liquid can be from the shift the absorption bands of at least two spectral sections determine where spectral ranges be picked out, where the difference of the Reflection spectrum between liquid and solid Physical state emerges particularly clearly and where the depth of penetration is sufficiently large namely in the order of magnitude usually Traffic or standing layers of water or ice. The one in the invention based on the desired Penetration depth influence of the subsurface, for example the road surface and a spread of the Material, for example the ice of the surface layer, is reflected by measuring the Radiation detected in two further wavelength ranges, that of an absorption of the molecules of the protic Liquid or solution regardless of that Degree of crystallization, can be influenced very little. The influence is then compensated for in the measurement evaluation.

It is advantageous to carry out the spectral analysis measurements both in front of and behind a wheel tread Vehicle and the evaluations then to each other in relation to what additional Statements, for example between slush and with layers of ice covered with a film of water can be.

By the measures specified in the subclaims are advantageous further developments and improvements possible.

Fig. 1

Reflexionsspektren für trocknen Asphalt, Asphalt mit Wasser und Asphalt mit Eis und

Fig. 2

eine schematische Darstellung der erfindungsgemäßen Vorrichtung.

An embodiment of the invention is shown in the drawing and is explained in more detail in the following description. Show it:

Fig. 1

Reflection spectra for dry asphalt, asphalt with water and asphalt with ice and

Fig. 2

a schematic representation of the device according to the invention.

In Fig. 1 are different reflection spectra for a wavelength range from approximately 850 nm to 1100 nm shown, with the upper spectrum for drying Asphalt, the medium spectrum for asphalt with water and the lower spectrum applies to asphalt with ice. Out The spectra show that certain Spectral values with the degree of crystallization to change. By measuring these spectral values statements about the degree of crystallization can thus be made make a road surface. For example, the absorption band of water among others at approx. 840 nm, 970 nm, 1170 nm and correspondingly for ice at 890 to 920 nm, 1020 to 1060 nm, 1260 to 1290 nm and so on.

Wasser:

980 nm - 2,17 cm; 1200 nm - 0,7 cm; 1450 nm - 0,035 cm; 1920 nm - 0,007 cm; und bei 3000 nm nur wenige µm.

Eis:

1030 nm - 3,102 cm; 1240 nm - 0,72 cm; 1490 nm - 0,022 cm; 1980 nm - 0,0097 cm; und bei 3000 nm gleichfalls nur wenige µm.

At these different wavelengths, radiation directed onto a water / ice layer can penetrate layers of different thicknesses before it is absorbed, that is to say the depth of penetration of the electromagnetic radiation into the layers changes with the wavelength. As an example, the penetration depths are given for some wavelengths in water and ice, whereby here the penetration depth is the depth at which the radiated light or the radiation has dropped to 1 / e:

Water:

980 nm - 2.17 cm; 1200 nm - 0.7 cm; 1450 nm - 0.035 cm; 1920 nm - 0.007 cm; and at 3000 nm only a few µm.

Ice cream:

1030 nm - 3.102 cm; 1240 nm - 0.72 cm; 1490 nm - 0.022 cm; 1980 nm - 0.0097 cm; and also only a few µm at 3000 nm.

From these values it can be seen that in the high wavelength range for example of 3000 nm only one extremely thin surface film can be detected, so that frozen cold cannot be determined. This is a common water layer on road surfaces or ice layer over its entire thickness can be must at low wavelengths Example up to 1300 nm can be measured. But when the wavelength ranges with sufficient, that is with a penetration depth of at least several millimeters, are chosen when measuring spectral Reflectance the spectral properties of the Road surface covered. As an example in Fig. 1 the spectral reflectance of asphalt is given, the spectral properties are fundamentally dependent are of the grain size. For different Road surfaces also change the spectra of reflectivity, but measurements of different Road surfaces have shown that the Reflectivity or the degrees of reflection in the wavelength range of interest in most relevant cases can be approximated linearly.

Since the spectral properties of the subsurface are included in the reflection measurements from wet or icy surfaces, they must be compensated for. In order to carry out this compensation, in the method according to the invention, reflection measurements are carried out at two wavelengths which are invariant to icing or crystallization in order to determine the background or background, and reflection measurements are also carried out at two wavelengths which / Carry ice information. In Fig. 1, the wavelengths for determining the background with λ _A and λ _D and the wavelengths with water / ice information with λ _B and λ _c , respectively.

The evaluation of a reflection measurement in the four wavelength ranges is discussed below. To determine the influence of the background, the slope of the background line is determined, the signal voltage at the wavelengths being denoted by S (λ): m = s (λ D ) - S (λ A ) divided by λ D - λ A . The background or background signal S _H at the wavelengths λ _B and λ _{c is} determined as follows: s H (λ B ) = s (λ A ) + m (λ B - λ A ) s H (λ C. ) - S (λ A ) + m (λ C. - λ A ). These background signals are subtracted from the actual signals at λ _B and λ _c to background-adjusted signals: s' (λ B ) = S (λ B ) - p H (λ B ) s' (λ C. ) = s (λ C. ) - p H (λ C. ). The reflectivity of the background causes the total level of backscattered light to fluctuate greatly, so the values s '(λ _B ) and s' (λ _c ) with the "medium brightness" s _G = s [λ _A ] + s [λ _D ] / 2 are standardized: S "(λ B ) = S '(λ B ) / P G and S "(λ C. ) = S '(λ C. ) / P G . The sum of S "(λ _B ) and s" (λ _c ) is a measure of the total amount of moisture present, that is to say for the total water molecules present. The difference between the two values (S "(λ _B ) - s" (λ _c ) and the quotient of the two values (S "(λ _B ) / S" (λ _c ) are both a measure of the proportion of the material that has already been frozen of the total amount of moisture or water molecules. S "(λ _B ) and S" (λ _c ) and their sum correlate with the thickness of a layer of water or ice, whereby the scatter in ice can be taken into account in the correlation thus estimate the thickness of layers of water and / or ice, even if both are present at the same time.

An advantageous embodiment of a measuring arrangement for carrying out the method according to the invention is shown schematically in FIG. 2. The electromagnetic radiation from a light or radiation source 1, for example a diffuse white light source with an infrared component sufficient for the measurement, is then applied to the surface 3 to be checked via a condenser lens 2. The portion of the electromagnetic radiation which is reflected by the surface 3, which will generally be a diffuse reflection, depending on the surface condition, is imaged on the entrance surface of a light guide 5 via a collecting optics 4, which, for example, precisely positions the radiation onto the surface Conducts receiver and evaluation units which are arranged, for example, in the interior of a motor vehicle. The radiation emerging from the light guide is simultaneously directed via a further condenser 6 to four receivers 7, the radiation being divided via three semi-transparent mirrors 8, each with 50% reflection and 50% transmission, and projected onto the receivers 7 via converging lenses 9. In this case, wavelength-selective filters 10, 11, 12, 13 are arranged in front of the converging lenses 9, which pass the wavelengths λ _A to λ _D of, for example, 920, 980, 1030 and 1080 nm.

The receivers 7 are equipped with an evaluation unit 14 connected by evaluating according to the above specified ratings is carried out. The exit the evaluation unit, which is designed as a microcomputer can be with a display unit and / or a warning device connected. The recipients 7 can be designed as discrete diodes can also be fast-responding, highly sensitive to light Arrays, such as diode arrays, CCD arrays or the like can be used. Important at the measurement is that the entire cross section of the from of the surface 3 to be viewed reflected Light beam mapped onto each receiver regardless of location is a location-independent evaluation can be made.

2 is only an example, it is also conceivable that instead of the semipermeable Mirror 8 and the wavelength selective filter a dispersion element that acts as a diffraction grating or Prism is formed, is provided on which the Radiation is split wavelength-selectively, the receivers, for example via light guides, locally assigned to the wavelengths on the diffraction grating are.

The evaluation unit 14 evaluates more depending on the or less present crystalline state of the Surface 3, i.e. here of the solid / liquid water, the reflected spectrum characteristic of this out. The evaluation can be according to the above Procedures are carried out step by step. The evaluation unit 14, however, the evaluation can be made on appropriate neural networks Algorithms, along with decision logic, which is based on fuzzy logic, that is, building on the theory of fuzzy sets, so that the possibility of evaluation at high Accuracy also for very blurred spectra images results. Based on the evaluation, too different thicknesses of water over ice or Slush can be recognized.

To avoid extraneous light and other influencing factors can intensity modulation of the light source 1 via a chopper wheel or electronic power control be made.

The measuring arrangement according to the invention is on a vehicle preferably arranged in the immediate vicinity of the track. Are two such measuring arrangements, and once in the direction of travel before the lane to the other provided behind the track in the direction of travel, so leave conclusions can also be drawn from comparative measurements pull, if necessary, not only on the risk of smoothness point out, but for example also to those that can arise from aquaplaning.

The device according to the invention can also be used to provide information about the micro-roughness of the road surface, since the ratio of the values m determined above (slope of the spectral curve of the background) and s _G (“average brightness”) is a measure of the wavelength dependence of the scattering capacity of the road surface. The largest part of this wavelength dependency has the grain size of the scattering particles (Mie scattering). m / S _G thus characterizes the micro-roughness of the road surface, which is essential for assessing tire grip on the road. This applies not only to dry topping, but also to snow, for example, since the grain size also varies here depending on the type of snow.

Claims (10)

1. Process for determining the surface state, in particular of highways with respect to dryness, wetness or icing, in which the surface is irradiated by a radiation source with an infrared component, and the reflected radiation is simultaneously measured in different wavelength ranges which characterise water and ice, and a statement regarding the surface state is made in dependence of the measured signals, characterised in that the reflected radiation is simultaneously and selectively measured in at least four wavelength ranges between 800 and 1,250 nm, and a first and a second wavelength range is chosen in such a manner that they are little influenced by absorption of the water molecules and independent of the state of the aggregate; and a third and fourth wavelength range is chosen in such a manner that they are characteristic for water and ice, and an influence of the base on signals measured in the third and fourth wavelength range as caused by the penetration depth is compensated by means of information given by signals measured in the first and second wavelength range.
2. Process according to Claim 1, characterised in that the third and fourth wavelength range is selected between 900 and 1,100 nm.
3. Process according to Claim 1 or 2, characterised in that the content of water and ice in the total moisture volume is determined from the ratio and/or the difference of the compensated signals.
4. Process according to one of Claims 1 to 3, characterised in that the total cross-section of radiation reflected from the surface is measured for each wavelength range independently from location.
5. Device for determining the surface state, in particular of highways with respect to dryness, wetness or icing, with a radiation source (1) with an infrared component for irradiation of the surface (3), a condenser optics (2) in the beampath ahead of the surface (3) to be tested, an optical array (4) which gathers the reflected portion of electro-magnetic radiation and a wavelength selective receiver arrangement (7 to 13) which receives the reflected radiation corresponding with a plurality of wavelength ranges, and an evaluation unit (14) for evaluation of wavelength selective signals, characterised in that the receiver arrangement (7 to 13) is provided for receiving radiation in four wavelength ranges between 800 and 1,250 nm, and a first and a second wavelength range is chosen so that they are little affected by an absorption of the water molecules, independently from the state of the aggregate; and a third and fourth wavelength range is selected so that they are characteristic of water and ice; and the evaluation unit (14) is provided for compensating an influence of the base on signals measured in the third and fourth wavelength range by means of information of signals measured in the first and second wavelength range.
6. Device according to Claim 5, characterised in that the receiver arrangement comprises three radiation splitters (8) for splitting reflected radiation into four beampaths of identical spatial information and four wavelength selective filters (10 to 13) in front of the respective receivers (7) with a forward wavelength range between 800 and 1,250 nm.
7. Device according to Claim 5, characterised in that the receiver arrangement comprises a spatially dispersive element in the form of at least one grid or prism which forms a wavelength selective diffraction spectrum in a wavelength range between 800 and 1,250 nm, and this dispersive element is spatially associated with receivers.
8. Device according to one of Claims 5 to 7, characterised in that the receivers are designed as array detectors.
9. Device according to one of Claims 5 to 8, characterised in that they are arranged on vehicles in front of and/or behind a vehicle track.
10. Use of the device according to one of Claims 5 to 9 for the purpose of determining the roughness of a highway surface layer.

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